Photovoltaic or solar cells are designed for converting solar radiation to electrical current. In concentrator solar photovoltaic applications, the incoming sunlight is optically concentrated before it is directed to solar cells. For example, the incoming sunlight is received by a primary mirror that reflects the received radiation toward a secondary mirror that, in turn, reflects the radiation toward a solar cell, which converts the concentrated radiation to electrical current by the generation of electron-hole pairs in III-V semiconductor or single crystal silicon, for example. Concentrator photovoltaics may, alternatively or additionally, comprise Fresnel lens optics for the concentration of the incoming solar radiation.
Since different semiconductor material compositions show optimal absorption for different wavelengths of the incoming solar radiation, multijunction cells have been proposed that comprise, for example, three cells showing optimal absorption in different wavelength ranges. The individual cells of the multijunction cell are electrically connected in series. Consequently, the particular cell having the lowest rate of generation of free charge carriers limits the overall power generation, i.e., the gained total current. This current matching is usually designed for the standard AM 1.5d ASTM 173-3 spectrum. However, the actual spectrum of the incoming solar light is time-dependent on scales from minutes or hours to months. In particular, the spectrum changes with seasons, day-time and weather conditions. Thus, the current matching results in significant performance losses due to the variability of the incoming solar light.
Thus, despite the recent engineering progress, there is still a need for a solar cell configuration that is only hardly affected by the temporally varying spectrum of incoming light.